Technical Field
The present disclosure relates to a spring assembly, particularly to a spring assembly and a damper device for absorbing and attenuating torsional vibration.
Background Information
In vehicles, spring assemblies are installed in a damper mechanism for, e.g., a clutch disc assembly, a flywheel assembly, a lock-up clutch for a torque converter, etc., so as to absorb and attenuate torsional vibration.
The spring assemblies are configured to elastically couple an input-side rotary member and an output-side rotary member in a circumferential direction. When the input-side rotary member and the output-side rotary member are rotated relatively to each other, the spring assemblies are configured to be compressed between the input-side rotary member and the output-side rotary member in a rotational direction. In this state, torsional vibration inputted into the input-side rotary member is absorbed and attenuated by the spring assemblies.
As an example of the spring assembly described above, there has been known a spring assembly including two coil springs on which one being nested in the other (see Japan Laid-open Patent Application Publication No. 2004-183871). The spring assembly includes an outer coil spring (a first coil spring) and an inner coil spring (a second coil spring). The inner coil spring is shorter than the outer coil spring and is disposed in the interior of the outer coil spring.
In the above conventional spring assembly, when the outer coil spring expands and contracts, and the inner coil spring doesn't expand and contract, the inner coil spring is movable on an inner peripheral side of the outer coil spring in a circumferential direction. In this state, when centrifugal force acts on the inner coil spring, the inner coil spring is in contact with an inner peripheral surface of the outer coil spring and slides on the inner peripheral surface in the circumferential direction.
There is possibility that an end portion of the inner coil spring abuts against a coil wire of the outer coil spring, and/or invades a gap between windings of the outer coil spring, while the inner coil spring slides on the inner peripheral surface of the outer coil spring.
To address these problems, there was an attempt to use a barrel-shaped inner coil spring. In this case, the above problems can be alleviated, but a new problem was caused by forming the inner coil spring in a barrel shape.
The problem is that an endmost winding (a first winding) of an end of the inner coil spring intrudes inside a second winding adjacent to the endmost winding, for example, when the end portion of the inner coil spring abuts against the outer coil spring and/or invades the outer coil spring.
In this case, it is likely that compressive strength of the inner coil spring can't achieve a desired compressive strength of the inner coil spring which a designer desires, because unanticipated bending stress generates in the end of the inner coil spring.
It is an object of the present disclosure to improve a durability of a second coil spring disposed on the inner peripheral side of a first coil spring.